Yes, you can definitely get big with oral steroids alone, you just have to know what you are doing. You have to take in consideration, drug half lifes, aromatization, dosage and most of all keep eating a lot of good food, train hard and sleep. (Just like you would have to without drugs.)
The reason guys here usually recommend testosterone based cycles is because it delivers good solid gains and the sides are more maintainable. Also, most guys wanting to take oral only cycles are usually the ones that have not trained long/hard enough and are looking for an "easy way out."
Ps. I'm not saying that you are one of those people...